* Adds lib/fixtures.rb, containing a Fixtures singleton object to use in testing.

* Uses Fixtures object to load TEAMS_ASSET_FILE and UOIS xml fixtures for tests in spec/fixtures/artesia/load_fixtures.rb.

* Renames spec/fixtures/teams_asset_files/ to spec/fixtures/artesia/ and renames the complete TEAMS_ASSET_FILE xml to teams_asset_file.xml inside of the respective thing they represent. E.g.:
  was: "spec/fixtures/teams_asset_files/zoom/zoom.xml"
  now renamed to: "spec/fixtures/artesia/zoom/teams_asset_file.xml"